Competition and facilitation may lead to asymmetric range shift dynamics with climate change

Dispersal abilities favor commensalism in animal-plant interactions under climate change

Scientists still poorly understand how biotic interactions and dispersal limitation jointly interact and affect the ability of species to track suitable habitats under climate change. Here, we examine how animal-plant interactions and dispersal limitations might affect the responses of Brazil nut-dependent frogs facing projected climate change. Using ecological niche modelling and dispersal simulations, we forecast the future distributions of the Brazil nut tree and three commensalist frog species over time (2030, 2050, 2070, and 2090) in the regional rivalry (SSP370) scenario that includes great challenges to mitigation and adaptation. With the exception of one species, projections point to a decrease in suitable habitats of up to 40.6%. For frog species with potential reductions of co-occurrence areas, this is expected to reduce up to 23.8% of suitable areas for binomial animal-plant relationships. Even so, biotic interactions should not be lost over time. Species will depend on their own dispersal abilities to reach analogous climates in the future for maintaining ecological and evolutionary processes associated with commensal taxa. However, ecological and evolutionary processes associated with commensal taxa should be maintained in accordance with their own dispersal ability. When dispersal limitation is included in the models, the suitable range of all three frog species is reduced considerably by the end of the century. This highlights the importance of dispersal limitation inclusion for forecasting future distribution ranges when biotic interactions matter.

Climate Variation within the Range of Longleaf Pine Forests during the Past Century

Longleaf pine (Pinus palustris Mill.) forests are an important ecosystem in the southeastern United States, with high economic and ecological value. It is necessary to study the climate variation within its range in order to understand the effects of climate change on longleaf pine forests. In this study, past climate data at three sites within the longleaf pine range were used to detect climate variation. The results indicated no dramatic change in solar radiation at the three sites. There were high variations in annual air temperature at the three sites. The trend of annual air temperature change depended on the time scale and start/end time. The annual air temperature generally increased from the 1960s at three sites. However, from 1901 to 2020, the trend of increasing annual air temperature was not consistent. The annual precipitation and the standardized precipitation-evapotranspiration index were relatively stable, with variation at the three sites. The regimes of annual and monthly air temperature and precipitation were not shifted based on the analysis of multiscale entropy. The climate niche of longleaf pine forests based on long-term climate data was broader than previously found. These results may be helpful to understand the interactions of the atmosphere and growth of longleaf pine forest and develop relevant management strategies.

Complex range shifts among forest functional types under the contemporary warming

The direction and magnitude of species distribution shifts tend to differ among species and functional types (FTs). Quantifying functional trait variation and species interactions will improve our understanding of the complex mechanisms that govern ecosystem dynamics and their responses to climate change. Here, we analyzed differences in the juvenile and adult temperature ranges of Japanese tree species at the mean, colder edge, and warmer edge of their distributions to reveal how functional traits affect interactions between different FT groups (e.g., deciduous and evergreen broad-leaved trees), using linear models and permutation tests. Overall, juveniles preferred cooler sites, but with high variation. The variation among species was partly explained by the difference in seed mass where species with lighter seeds tend to colonize colder sites. On the other hand, the distribution range of FTs showed complex behavior at the ecotones of different FTs. Specifically, in three of eight ecotones, nonparallel range shifts between FTs were detected, which includes cold shifting in deciduous broad-leaved FT where a warm shift by subalpine FT happened, and cold shifting in subtropical FT where warm shifts by either the deciduous broad-leaved or the evergreen broad-leaved FTs happened. Our results suggest that past warming has caused a general cold shift at species level, whereas different mechanisms, such as light seeds disperse farther in distribution's colder edge and heavy seeds (e.g., evergreen broad-leaved) compete better in warmer edge, create nonparallel responses of FT distribution ranges leading to the observed homogenization at several ecotones among FTs. These complex range shifts at FT level have crucial implications for climate change mitigation and adaptation.

Forest fires and climate-induced tree range shifts in the western US

Due to climate change, plant populations experience environmental conditions to which they are not adapted. Our understanding of the next century's vegetation geography depends on the distance, direction, and rate at which plant distributions shift in response to a changing climate. In this study we test the sensitivity of tree range shifts (measured as the difference between seedling and mature tree ranges in climate space) to wildfire occurrence, using 74,069 Forest Inventory Analysis plots across nine states in the western United States. Wildfire significantly increased the seedling-only range displacement for 2 of the 8 tree species in which seedling-only plots were displaced from tree-plus-seedling plots in the same direction with and without recent fire. The direction of climatic displacement was consistent with that expected for warmer and drier conditions. The greater seedling-only range displacement observed across burned plots suggests that fire can accelerate climate-related range shifts and that fire and fire management will play a role in the rate of vegetation redistribution in response to climate change.

Why Are Species’ Traits Weak Predictors of Range Shifts?

We examine the evidence linking species’ traits to contemporary range shifts and find they are poor predictors of range shifts that have occurred over decades to a century. We then discuss reasons for the poor performance of traits for describing interspecific variation in range shifts from two perspectives: ( a) factors associated with species’ traits that degrade range-shift signals stemming from the measures used for species’ traits, traits that are typically not analyzed, and the influence of phylogeny on range-shift potential and ( b) issues in quantifying range shifts and relating them to species’ traits due to imperfect detection of species, differences in the responses of altitudinal and latitudinal ranges, and emphasis on testing linear relationships between traits and range shifts instead of nonlinear responses. Improving trait-based approaches requires a recognition that traits within individuals interact in unexpected ways and that different combinations of traits may be functionally equivalent.

Rules of Plant Species Ranges: Applications for Conservation Strategies

Earth is changing rapidly and so are many plant species’ ranges. Here, we synthesize eco-evolutionary patterns found in plant range studies and how knowledge of species ranges can inform our understanding of species conservation in the face of global change. We discuss whether general biogeographic “rules” are reliable and how they can be used to develop adaptive conservation strategies of native plant species across their ranges. Rules considered include (1) factors that set species range limits and promote range shifts; (2) the impact of biotic interactions on species range limits; (3) patterns of abundance and adaptive properties across species ranges; (4) patterns of gene flow and their implications for genetic rescue, and (5) the relationship between range size and conservation risk. We conclude by summarizing and evaluating potential species range rules to inform future conservation and management decisions. We also outline areas of research to better understand the adaptive capacity of plants under environmental change and the properties that govern species ranges. We advise conservationists to extend their work to specifically consider peripheral and novel populations, with a particular emphasis on small ranges. Finally, we call for a global effort to identify, synthesize, and analyze prevailing patterns or rules in ecology to help speed conservation efforts.

Tree recruitment is determined by stand structure and shade tolerance with uncertain role of climate and water relations

Tree regeneration is a key process for long-term forest dynamics, determining changes in species composition and shaping successional trajectories. While tree regeneration is a highly stochastic process, tree regeneration studies often cover narrow environmental gradients only, focusing on specific forest types or species in distinct regions. Thus, the larger-scale effects of temperature, water availability, and stand structure on tree regeneration are poorly understood.We investigated these effects in respect of tree recruitment (in-growth) along wide environmental gradients using forest inventory data from Flanders (Belgium), northwestern Germany, and Switzerland covering more than 40 tree species. We employed generalized linear mixed models to capture the abundance of tree recruitment in response to basal area, stem density, shade casting ability of a forest stand as well as site-specific degree-day sum (temperature), water balance, and plant-available water holding capacity. We grouped tree species to facilitate comparisons between species with different levels of tolerance to shade and drought.Basal area and shade casting ability of the overstory had generally a negative impact on tree recruitment, but the effects differed between levels of shade tolerance of tree recruitment in all study regions. Recruitment rates of very shade-tolerant species were positively affected by shade casting ability. Stem density and summer warmth (degree-day sum) had similar effects on all tree species and successional strategies. Water-related variables revealed a high degree of uncertainty and did not allow for general conclusions. All variables had similar effects independent of the varying diameter thresholds for tree recruitment in the different data sets.Synthesis: Shade tolerance and stand structure are the main drivers of tree recruitment along wide environmental gradients in temperate forests. Higher temperature generally increases tree recruitment rates, but the role of water relations and drought tolerance remains uncertain for tree recruitment on cross-regional scales.

Differential Tolerance and Seasonal Adaptation to Temperature and Salinity Stress at a Dynamic Range Boundary Between Estuarine Gastropods

AbstractInsight into how coastal organisms will respond to changing temperature and salinity regimes may be derived from studies of adaptation to fluctuating estuarine environments, especially under stressful range-edge conditions. We characterized a dynamic range boundary between two estuarine sea slugs, Alderia modesta (distributed across the North Pacific and North Atlantic) and Alderia willowi, known from southern and central California. The species overlap from Bodega Bay to San Francisco Bay, where populations are dominated by A. modesta after winter rains but by A. willowi after peak summer temperatures. Laboratory assays confirmed superior tolerance to low salinity for the northern species, A. modesta: encapsulated embryos developed at 8 ppt, larvae survived at 4-6 ppt, and adults survived repeated exposure to 2 ppt, salinities that reduced development or survival for the same stages of A. willowi. Adults did not appreciably differ in their high-temperature threshold, however. Each species showed increased tolerance to either temperature or salinity stress at its range margin, indicating plasticity or local adaptation, but at the cost of reduced tolerance to the other stressor. At its northern limit, A. willowi became more tolerant of low salinity during the winter rainy season, but also less heat tolerant. Conversely, A. modesta became more heat resistant from spring to summer at its southern limit, but less tolerant of low salinity. Trade-offs in stress tolerance may generally constrain adaptation and limit biotic response to a rapidly changing environment, as well as differentiating species niches.

Climate-driven range shifts reduce persistence of competitors in a perennial plant community

Forecasting the impacts of climate change on species persistence in diverse natural communities requires a way to account for indirect effects mediated through species interactions. In particular, we expect species to experience major changes in competition as they track favorable climates. Here, we combine experimental data with a recently developed theoretical framework based on coexistence theory to measure the impact of climate-driven range shifts on alpine plant persistence under climate change. We transplanted three co-dominant alpine perennial species to five elevations, creating a maximum of 5°C increase in average growing-season temperature. We statistically modeled species' demographic rates in response to the environment and interpolated species' intrinsic ranges-the environmental mapping of reproduction in the absence of competition. We used low-density population growth rates-species' initial rate of invasion into an established community-as a metric of persistence. Further analysis of low-density growth rates (LGRs) allowed us to parse the direct impacts of climate change from indirect impacts mediated by shifting competition. Our models predict qualitatively different range shifts for each species based on the climate conditions under which growth rates are maximized and where they are zero. Overall, climate change is predicted to increase the intrinsic (competition free) growth rates of all species, as warmer and wetter conditions increase the favorability of alpine habitat. However, these benefits are entirely negated by increased competition arising from greater overlap between competitors in their intrinsic ranges. Species were highly dispersal limited, which can prevent species from tracking shifting intrinsic ranges by reducing population spread rates. Yet dispersal limitation also promoted species' persistence because it promotes persistence mechanisms. Our study demonstrates the complex pathways by which climate change impacts species' persistence by altering their competitive environment, and highlights how a persistence framework based on LGRs can help disentangle impacts.

Improvements in reports of species redistribution under climate change are required

Studies have documented climate change-induced shifts in species distributions but uncertainties associated with data and methods are typically unexplored. We reviewed 240 reports of climate-related species-range shifts and classified them based on three criteria. We ask whether observed distributional shifts are compared against random expectations, whether multicausal factors are examined on equal footing, and whether studies provide sufficient documentation to enable replication. We found that only ~12.1% of studies compare distributional shifts across multiple directions, ~1.6% distinguish observed patterns from random expectations, and ~19.66% examine multicausal factors. Last, ~75.5% of studies report sufficient data and results to allow replication. We show that despite gradual improvements over time, there is scope for raising standards in data and methods within reports of climate-change induced shifts in species distribution. Accurate reporting is important because policy responses depend on them. Flawed assessments can fuel criticism and divert scarce resources for biodiversity to competing priorities.

Climate Change and Local Host Availability Drive the Northern Range Boundary in the Rapid Expansion of a Specialist Insect Herbivore, Papilio cresphontes

Species distributions, abundance, and interactions have always been influenced by human activity and are currently experiencing rapid change. Biodiversity benchmark surveys traditionally require intense human labor inputs to find, identify, and record organisms limiting the rate and impact of scientific enquiry and discovery. Recent emergence and advancement of monitoring technologies have improved biodiversity data collection to a scale and scope previously unimaginable. Community science web platforms, smartphone applications, and technology assisted identification have expedited the speed and enhanced the volume of observational data all while providing open access to these data worldwide. How to integrate and leverage the data into valuable information on how species are changing in space and time requires new best practices in computational and analytical approaches. Here we integrate data from three community science repositories to explore how a specialist herbivore distribution changes in relation to host plant distributions and other environmental factors. We generate a series of temporally explicit species distribution models to generate range predictions for a specialist insect herbivore (Papilio cresphontes) and three predominant host-plant species. We find that this insect species has experienced rapid northern range expansion, likely due to a combination of the range of its larval host plants and climate changes in winter. This case study shows rapid data collection through large scale community science endeavors can be leveraged through thoughtful data integration and transparent analytic pipelines to inform how environmental change impacts where species are and their interactions for a more cost effective method of biodiversity benchmarking.

Continent-wide tree fecundity driven by indirect climate effects

Indirect climate effects on tree fecundity that come through variation in size and growth (climate-condition interactions) are not currently part of models used to predict future forests. Trends in species abundances predicted from meta-analyses and species distribution models will be misleading if they depend on the conditions of individuals. Here we find from a synthesis of tree species in North America that climate-condition interactions dominate responses through two pathways, i) effects of growth that depend on climate, and ii) effects of climate that depend on tree size. Because tree fecundity first increases and then declines with size, climate change that stimulates growth promotes a shift of small trees to more fecund sizes, but the opposite can be true for large sizes. Change the depresses growth also affects fecundity. We find a biogeographic divide, with these interactions reducing fecundity in the West and increasing it in the East. Continental-scale responses of these forests are thus driven largely by indirect effects, recommending management for climate change that considers multiple demographic rates.

Seed quality and seed quantity in red maple depends on weather and individual tree characteristics

Under future climate change, plant species are expected to shift their ranges in response to increasing temperatures and altered precipitation patterns. As seeds represent the single opportunity for plants to move, it is critical to quantify the factors that influence reproduction. While total seed production is clearly important, seed quality is equally as critical and often overlooked. Thus, to quantify how environmental and tree-level characteristics affect seed quality and quantity, the reproductive output of red maple (Acer rubrum) was measured along an elevation gradient in the Monongahela National Forest, WV. A variety of individual-level characteristics were measured (e.g., DBH, canopy area, height, and tree cores were taken to quantify growth), and seed traps were placed under seed-bearing trees to collect samaras and quantify total seed production. A random subsample of collected seeds from each tree was micro-CT scanned to determine embryo volume, photographed for morphology measurements, and used for germination trials. The number of seeds produced was negatively affected by frost events during flowering, and stand density. The trees with the most seeds also showed reduced growth in recent years. Only 63% of scanned seeds showed embryo development, and of those seeds-only 23% germinated. The likelihood of embryo presence increased as growth rate decreased, while embryo size increased with tree height, smaller DBH, and in areas dominated by hemlock. Both larger embryo volume and larger overall seed size increased the likelihood of germination. The results highlight the importance of including seed quality in addition to seed quantity for a more complete representation of reproductive output.

Biotic rescaling reveals importance of species interactions for variation in biodiversity responses to climate change

Generality in understanding biodiversity responses to climate change has been hampered by substantial variation in the rates and even directions of response to a given change in climate. We propose that such context dependencies can be clarified by rescaling climate gradients in terms of the underlying biological processes, with biotic interactions as a particularly important process. We tested this rescaling approach in a replicated field experiment where entire montane grassland communities were transplanted in the direction of expected temperature and/or precipitation change. In line with earlier work, we found considerable variation across sites in community dynamics in response to climate change. However, these complex context dependencies could be substantially reduced or eliminated by rescaling climate drivers in terms of proxies of plant-plant interactions. Specifically, bryophytes limited colonization by new species into local communities, whereas the cover of those colonists, along with bryophytes, were the primary drivers of local extinctions. These specific interactions are relatively understudied, suggesting important directions for future work in similar systems. More generally, the success of our approach in explaining and simplifying landscape-level variation in climate change responses suggests that developing and testing proxies for relevant underlying processes could be a fruitful direction for building more general models of biodiversity response to climate change.

Longer photoperiods through range shifts and artificial light lead to a destabilizing increase in host-parasitoid interaction strength

Many organisms are experiencing changing daily light regimes due to latitudinal range shifts driven by climate change and increased artificial light at night (ALAN). Activity patterns are often driven by light cycles, which will have important consequences for species interactions. We tested whether longer photoperiods lead to higher parasitism rates by a day-active parasitoid on its host using a laboratory experiment in which we independently varied daylength and the presence of ALAN. We then tested whether reduced nighttime temperature tempers the effect of ALAN. We found that parasitism rate increased with daylength, with ALAN intensifying this effect only when the temperature was not reduced at night. The impact of ALAN was more pronounced under short daylength. Increased parasitoid activity was not compensated for by reduced life span, indicating that increased daylength leads to an increase in total parasitism effects on fitness. To test the significance of increased parasitism rate for population dynamics, we developed a host-parasitoid model. The results of the model predicted an increase in time-to-equilibrium with increased daylength and, crucially, a threshold daylength above which interactions are unstable, leading to local extinctions. Here we demonstrate that ALAN impact interacts with daylength and temperature by changing the interaction strength between a common day-active consumer species and its host in a predictable way. Our results further suggest that range expansion or ALAN-induced changes in light regimes experienced by insects and their natural enemies will result in unstable dynamics beyond key tipping points in daylength.

Temporal lags in observed and dark diversity in the Anthropocene

Understanding biodiversity changes in the Anthropocene (e.g. due to climate and land-use change) is an urgent ecological issue. This important task is challenging because global change effects and species responses are dependent on the spatial scales considered. Furthermore, responses are often not immediate. However, both scale and time delay issues can be tackled when, at each study site, we consider dynamics in both observed and dark diversity. Dark diversity includes those species in the region that can potentially establish and thrive in the local sites' conditions but are currently locally absent. Effectively, dark diversity connects biodiversity at the study site to the regional scales and defines the site-specific species pool (observed and dark diversity together). With dark diversity, it is possible to decompose species gains and losses into two space-related components: one associated with local dynamics (species moving from observed to dark diversity and vice versa) and another related to gains and losses of site-specific species pool (species moving to and from the pool after regional immigration, regional extinction or change in local ecological conditions). Extinction debt and immigration credit are useful to understand dynamics in observed diversity, but delays might happen in species pool changes as well. In this opinion piece we suggest that considering both observed and dark diversity and their temporal dynamics provides a deeper understanding of biodiversity changes. Considering both observed and dark diversity creates opportunities to improve conservation by allowing to identify species that are likely to go regionally extinct as well as foreseeing which of the species that newly arrive to the region are more likely to colonize local sites. Finally, by considering temporal lags and species gains and losses in observed and dark diversity, we combine phenomena at both spatial and temporal scales, providing a novel tool to examine biodiversity change in the Anthropocene.

Density-dependence tips the change of plant-plant interactions under environmental stress

Facilitation studies typically compare plants under differential stress levels with and without neighbors, while the density of neighbors has rarely been addressed. However, recent empirical studies indicate that facilitation may be density-dependent too and peak at intermediate neighbor densities. Here, we propose a conceptual model to incorporate density-dependence into theory about changes of plant-plant interactions under stress. To test our predictions, we combine an individual-based model incorporating both facilitative response and effect, with an experiment using salt stress and Arabidopsis thaliana. Theoretical and experimental results are strikingly consistent: (1) the intensity of facilitation peaks at intermediate density, and this peak shifts to higher densities with increasing stress; (2) this shift further modifies the balance between facilitation and competition such that the stress-gradient hypothesis applies only at high densities. Our model suggests that density-dependence must be considered for predicting plant-plant interactions under environmental change.

Interactive range-limit theory (iRLT): An extension for predicting range shifts

A central theme of range-limit theory (RLT) posits that abiotic factors form high-latitude/altitude limits, whereas biotic interactions create lower limits. This hypothesis, often credited to Charles Darwin, is a pattern widely assumed to occur in nature. However, abiotic factors can impose constraints on both limits and there is scant evidence to support the latter prediction. Deviations from these predictions may arise from correlations between abiotic factors and biotic interactions, as a lack of data to evaluate the hypothesis, or be an artifact of scale. Combining two tenets of ecology-niche theory and predator-prey theory-provides an opportunity to understand how biotic interactions influence range limits and how this varies by trophic level. We propose an expansion of RLT, interactive RLT (iRLT), to understand the causes of range limits and predict range shifts. Incorporating the main predictions of Darwin's hypothesis, iRLT hypothesizes that abiotic and biotic factors can interact to impact both limits of a species' range. We summarize current thinking on range limits and perform an integrative review to evaluate support for iRLT and trophic differences along range margins, surveying the mammal community along the boreal-temperate and forest-tundra ecotones of North America. Our review suggests that range-limit dynamics are more nuanced and interactive than classically predicted by RLT. Many (57 of 70) studies indicate that biotic factors can ameliorate harsh climatic conditions along high-latitude/altitude limits. Conversely, abiotic factors can also mediate biotic interactions along low-latitude/altitude limits (44 of 68 studies). Both scenarios facilitate range expansion, contraction or stability depending on the strength and the direction of the abiotic or biotic factors. As predicted, biotic interactions most often occurred along lower limits, yet there were trophic differences. Carnivores were only limited by competitive interactions (n = 25), whereas herbivores were more influenced by predation and parasitism (77%; 55 of 71 studies). We highlight how these differences may create divergent range patterns along lower limits. We conclude by (a) summarizing iRLT; (b) contrasting how our model system and others fit this hypothesis and (c) suggesting future directions for evaluating iRLT.

High Temperature can Change Root System Architecture and Intensify Root Interactions of Plant Seedlings

Climate change could alter plant aboveground and belowground resource allocation. Compared with shoots, we know much less about how roots, especially root system architecture (RSA) and their interactions, may respond to temperature changes. Such responses could have great influence on species'acquisition of resources and their competition with neighbors. We used a gel-based transparent growth system to in situ observe the responses of RSA and root interactions of three common subtropical plant species seedlings in Asia differing in growth forms (herb, shrub, and tree) under a wide growth temperature range of 18-34°C, including low and supra-optimal temperatures. Results showed that the RSA, especially root depth and root width, of the three species varied significantly in response to increased temperature although the response of their aboveground shoot traits was very similar. Increased temperature was also observed to have little impact on shoot/root resource allocation pattern. The variations in RSA responses among species could lead to both the intensity and direction change of root interactions. Under high temperature, negative root interactions could be intensified and species with larger root size and fast early root expansion had competitive advantages. In summary, our findings indicate that greater root resilience play a key role in plant adapting to high temperature. The varied intensity and direction of root interactions suggest changed temperatures could alter plant competition. Seedlings with larger root size and fast early root expansion may better adapt to warmer climates.

The role of geography, environment, and genetic divergence on the distribution of pikas in the Himalaya

Pikas (Ochotona Link, 1795) are high-altitude specialist species making them a useful bioindicator species to warming in high-altitude ecosystem. The Himalayan Mountains are an important part of their range, supporting approximately 23%-25% of total pika species worldwide, yet we lack basic information on the distribution patterns. We combine field-based surveys with genetics-based identification and phylogeny to identify differences in species-environment relationships. Further, we suggest putative evolutionary causes for the observed niche patterns.

LOCATION

Himalayan high-altitude region.

METHODS

We sampled 11 altitudinal transects (ranging from ~2,000 to 5,000 m) in the Himalaya to establish occurrence records. We collected 223 species records using genetic analyses to confirm species' identity (based on some invasive and mostly noninvasive biological samples). Niche and geographic overlap were estimated using kernel density estimates.

RESULTS

Most pikas in the Himalaya span wide elevation ranges and exhibit extensive spatial overlap with other species. However, even in areas of high species diversity, we found species to have a distinct environmental niche. Despite apparent overlapping distributions at broad spatial scales, in our field surveys, we encountered few cases of co-occurrence of species in the sampled transects. Deeply diverged sister-species pair had the least environmental niche overlap despite having the highest geographic range overlap. In contrast, sister-species pair with shallow genetic divergence had a higher environmental niche overlap but was geographically isolated. We hypothesize that the extent of environmental niche divergence in pikas is a function of divergence time within the species complex. We assessed vulnerability of species to future climate change using environmental niche and geographic breadth sizes as a proxies. Our findings suggest that O. sikimaria may be the most vulnerable species. Ochotona roylii appears to have the most unique environmental niche space, with least niche overlap with other pika species from the study area.

Biophysical Gradients and Performance of Whitebark Pine Plantings in the Greater Yellowstone Ecosystem

Research Highlights: The efficacy of planting for restoration is important for ecosystem managers. Planting efforts represent an opportunity for conserving and managing species during a population crisis. Background and Objectives: Federal agencies have been planting whitebark pine (WBP), an important subalpine species that is late to mature and long-lived, for three decades in the Greater Yellowstone Ecosystem (GYE). These efforts have been met with varying success, and they have not been evaluated beyond the first five years post-planting. Ecosystem managers will continue to plant WBP in the GYE for years to come, and this research helps to inform and identify higher quality habitat during a period of changing climate and high GYE WBP mortality rates. Materials and Methods: We use a combination of field sampling and a water balance model to investigate local biophysical gradients as explanatory variables for WBP performance at twenty-nine GYE planting sites. Results: We found that the WBP growth rate was positively correlated with actual evapotranspiration (AET) and was greatest when cumulative growing season AET was above 350 mm. Growth rate was not strongly affected by competition at the levels found in this study. However, site density change over time was negatively affected by mean growing season temperature and when more than five competitors were present within 3.59 m radius. Conclusions: If they make it to maturity, trees that are planted this season will not begin to produce cones until the latter half of this century. We recommend planting efforts that optimize AET for growth rate objectives, minimize water deficit (WD) that cause stress and mortality, and removing competitors if they exceed five within a short distance of seedlings.

When facilitation meets clonal integration in forest canopies

Few studies have explored how - within the same system - clonality and positive plant-plant interactions might interact to regulate plant community composition. Canopy-dwelling epiphytes in species-rich forests provide an ideal system for studying this because many epiphytic vascular plants undertake clonal growth and because vascular epiphytes colonize canopy habitats after the formation of nonvascular epiphyte (i.e. bryophyte and lichen) mats. We investigated how clonal integration of seven dominant vascular epiphytes influenced inter-specific interactions between vascular epiphytes and nonvascular epiphytes in a subtropical montane moist forest in southwest China. Both clonal integration and environmental buffering from nonvascular epiphytes increased survival and growth of vascular epiphytes. The benefits of clonal integration for vascular epiphytes were higher when nonvascular epiphytes were removed. Similarly, facilitation from nonvascular epiphytes played a more important role when clonal integration of vascular epiphytes was eliminated. Overall, clonal integration had greater benefits than inter-specific facilitation. This study provides novel evidence for interactive effects of clonality and facilitation between vascular and nonvascular species, and has implications for our understanding of a wide range of ecosystems where both high levels of clonality and facilitation are expected to occur.

Disturbance and the elevation ranges of woody plant species in the mountains of Costa Rica

AIM

To understand how disturbance-here defined as a transient reduction in competition-can shape plant distributions along elevation gradients. Theory suggests that disturbance may increase elevation ranges, especially at the lower range limits, through reduced competitive exclusion. Nevertheless, to date this relationship remains unclear.

LOCATION

Mountains of Costa Rica.

METHODS

We compared the elevation range of woody stems over 10 cm dbh ("trees") observed in plots along two transects spanning a range of elevations in secondary (regrowth) and old-growth forest (409 and 249 species, respectively). We also estimated these elevation ranges using nationwide data. In addition, we examined the influence of stem size and plot scale basal area (as a measure of competition) on species elevation range limits in the two gradients.

RESULTS

In general, tree species ranges increased with elevation. Species in the secondary forest had broader elevation ranges (100-318 m broader than species in the old-growth forest; Wilcoxon: p-value <.001). Also, in the secondary transect, individuals with greater diameters had broader elevation ranges than those observed as smaller trees (137 m broader; Kruskal-Wallis: p-value = .03). The lower range limit of species occurred more frequently in plots with lower (vs. higher) basal area than expected by chance in both forest types. We also observed higher elevation upper limits in old growth, but not in secondary forests, with lower (vs. higher) basal area.

MAIN CONCLUSION

Disturbance relaxes the constraints imposed by competition and extends effective elevation ranges of species, particularly those in secondary forest, to warmer and cooler climates (minimum increase equivalent to about 0.6-1.4°C). Thus, suitable disturbance may assist species persistence under climate change. We believe this is the first study indicating a consistent relation between disturbance and woody plant species distributions along elevation gradients.

Chloroplast population genetics reveals low levels of genetic variation and conformation to the central-marginal hypothesis in Taxus wallichiana var. mairei, an endangered conifer endemic to China

The central-marginal hypothesis predicts that geographically peripheral populations should exhibit reduced genetic diversity and increased genetic differentiation than central populations due to smaller effective population size and stronger geographical isolation. We evaluated these predictions in the endangered conifer Taxus wallichiana var. mairei. Eight plastid simple sequence repeats (cpSSRs) were used to investigate plastid genetic variation in 22 populations of Taxus wallichiana var. mairei, encompassing nearly its entire distribution range. Low levels of plastid genetic variation and differentiation were detected in the populations, and the findings were attributed to low mutation rates, small population sizes, habitat fragmentation and isolation, and effective pollen or seed dispersal. Hunan and Hubei were identified as major refugia based on the number of private haplotypes and species distribution modeling. Trends in plastid genetic diversity and genetic differentiation from central to peripheral populations supported the predictions of the central-marginal hypothesis. In scenarios wherein the future climate becomes warmer, we predict that some peripheral populations will disappear and southern and southeastern regions will become significantly less habitable. Factors that include the levels of precipitation during the driest month, annual precipitation level, and annual temperature range will be decisive in shaping the future distribution of these populations. This study provides a theoretical basis for the conservation of T. wallichiana var. mairei.

Maladaptation beyond a geographic range limit driven by antagonistic and mutualistic biotic interactions across an abiotic gradient

Species' geographic range limits often result from maladaptation to the novel environments beyond the range margin. However, we rarely know which aspects of the n-dimensional environment are driving this maladaptation. Especially of interest is the influence of abiotic versus biotic factors in delimiting species' distributions. We conducted a 2-year reciprocal transplant experiment involving manipulations of the biotic environment to explore how spatiotemporal gradients in precipitation, fatal mammalian herbivory, and pollination affected lifetime fitness within and beyond the range of the California annual plant, Clarkia xantiana ssp. xantiana. In the first, drier year of the experiment, fitness outside the range edge was limited mainly by low precipitation, and there was some evidence for local adaptation within the range. In the second, wetter year, we did not observe abiotic limitations to plant fitness outside the range; instead biotic interactions, especially herbivory, limited fitness outside the range. Together, protection from herbivory and supplementation of pollen resulted in three- to sevenfold increases in lifetime fitness outside the range margin in the abiotically benign year. Overall, our work demonstrates the importance of biotic interactions, particularly as they interact with the abiotic environment, in determining fitness beyond geographic range boundaries.

Ocean currents modify the coupling between climate change and biogeographical shifts

Biogeographical shifts are a ubiquitous global response to climate change. However, observed shifts across taxa and geographical locations are highly variable and only partially attributable to climatic conditions. Such variable outcomes result from the interaction between local climatic changes and other abiotic and biotic factors operating across species ranges. Among them, external directional forces such as ocean and air currents influence the dispersal of nearly all marine and many terrestrial organisms. Here, using a global meta-dataset of observed range shifts of marine species, we show that incorporating directional agreement between flow and climate significantly increases the proportion of explained variance. We propose a simple metric that measures the degrees of directional agreement of ocean (or air) currents with thermal gradients and considers the effects of directional forces in predictions of climate-driven range shifts. Ocean flows are found to both facilitate and hinder shifts depending on their directional agreement with spatial gradients of temperature. Further, effects are shaped by the locations of shifts in the range (trailing, leading or centroid) and taxonomic identity of species. These results support the global effects of climatic changes on distribution shifts and stress the importance of framing climate expectations in reference to other non-climatic interacting factors.